1. Field of the Invention
This invention relates to a data-transmission system, data-transmission method and data-transmission apparatus that together with making it difficult to decode data that leaks during transmission, makes it possible to avoid problems that may occur due to transmission from a third party impersonating the true sender.
2. Description of the Related Art
Conventionally, technology has existed in which data to be sent by a sender is encrypted, and that encrypted data and an encryption key for decoding that encrypted data are sent to the recipient using separate lines (for example, a satellite communication line and ground line). (Refer to Japanese Patent No. 3,052,322)
The recipient receives the encrypted data and encryption key, and from these is able to decode the data into the original data. By sending the encrypted data and encryption key using separate lines in this way, it is possible to improve confidentiality of the data transmission.
However, since the recipient receives the data without authenticating the sender of the encryption key and encrypted data, it has not been possible to authenticate the sent data even in the case when sent by a third party that poses as the sender who originally sent the data.
For communication lines such as the Internet, individual-authentication services are available from authentication-service companies that perform individual authentication. However, the individual-authentication services provided by this kind of authentication service company are expensive, and thus have not been suitable for individual use.